As theory turns into fact

Remember the debate over acid rain? We're at it again with greenhouse gas emissions

BURLINGTON, Vt. — Snow fell early this fall on Camel's Hump, the third-highest peak in Vermont's Green Mountains and a galvanizing symbol of America's troubles with acid rain.

It was here almost three decades ago that botanists discovered the rapid decline of spruce, birch and maple trees that once grew so dense the canopy blotted out the sun. Gone were 30 percent of the trees that had been standing when researchers first surveyed the mountain in the mid-1960s, including half of the red spruce.

The alarming discovery led many scientists to conclude that the culprits were vehicles and coal-fired power plants. When mixed with water vapor in the clouds, pollution from tailpipes and smokestacks fell back in a caustic mist that slowly killed great forests and turned once-pristine lakes into dead seas.

"It was staggering what was happening," Hubert Vogelmann, the University of Vermont researcher who drew the nation's attention to Camel's Hump, said during a recent hike up the storied peak. "The evidence pointing to acid rain kept getting stronger and stronger. But it took some time before something was done about it."

Years from now, people might say the same thing about global warming.

The details are different. But there are similarities between the current debate about whether greenhouse gas emissions should be regulated and the scientific and political battles that eventually led Congress to adopt tougher limits on the pollution that causes acid rain.

The chief sources are the same. Coal-fired power plants and cars are the leading producers of carbon dioxide, the most prevalent greenhouse gas that prevents the sun's heat from radiating back into space.

Nearly all the experts who delve into the arcane history of Earth's climate agree that human activities -- mainly the burning of coal, oil and other fossil fuels -- are driving up global temperatures. The planet's average surface temperature has increased more than 1 degree Fahrenheit since 1990, and the rate of warming is rapidly increasing.

Many climate scientists think that if action isn't taken soon to reduce greenhouse gases, or at least slow their growth, weather shifts, coastal flooding, prolonged droughts and deadly heat waves could occur.

But there is still some uncertainty, just as there was about acid rain during the 1970s and '80s. And like that earlier debate, the scientific consensus about global warming doesn't amount to an airtight case for action, especially when there are still dissenters and vested economic interests are at stake.

A decade later, action

By the early 1980s, the science about acid rain was good enough that federal officials could pinpoint the sources of pollution. Yet nothing was done for almost another decade.

Utilities and other industries spent millions on lobbying and advertising campaigns to block tougher clean-air laws. One full-page ad in The New York Times envisioned a world covered in sludge from scrubbers--equipment that removes sulfur dioxide from power plant emissions. Business-friendly allies in the Reagan administration and Congress bottled up legislation to address acid rain, insisting that more study was needed.

Vogelmann and others figured one of the best ways to convert skeptics was to bring them to Camel's Hump. Politicians and bureaucrats hiked up the mountain, stopping occasionally along a rocky trail to take note of the dead and dying trees.

The field trips always included a demonstration. Vogelmann used a hand crank to pull samples from the trunk of a red spruce, showing how the tree's growth had suddenly been stunted by the acidic pollution.

"We kept coming back to the same tree," Vogelmann joked during the more recent hike. "So many people came to see what was happening that it was full of holes by the time Congress took action."

When President George H.W. Bush was elected in 1988, images of dying forests and lakes had become so potent that he vowed acid rain would top his agenda.

"The science got better, various states and other institutions started taking action, and suddenly there were political reasons to take on this issue," said David Hawkins, director of the Natural Resources Defense Council's Climate Center and a former top official at the U.S. Environmental Protection Agency.

Some continued to resist. One top utility executive ominously predicted that tougher clean-air laws would lead to "the potential destruction of the Midwest economy."

But two years after Bush took office, Congress and the EPA set up a system that put a nationwide limit on sulfur dioxide emissions while letting utilities trade the right to pollute.

Known as "cap-and-trade," the system turned sulfur dioxide into a commodity traded like pork bellies or grain futures. Cleaner power plants can sell credits, or pollution allowances, to dirtier sources as long as they all stay within the overall limit.